The present invention relates generally to textile products, and more particularly to textile products constructed using threadless sewing systems and processes for producing the same.
Several factors can limit production speeds of textile products using conventional sewing technology. Currently, one limiting factor is the operation speed of sewing equipment. So called xe2x80x9cthreadlessxe2x80x9d or xe2x80x9csimulatedxe2x80x9d sewing operations using various adhesive systems as a substitute for textile thread to join fabric surfaces have been proposed in an attempt to overcome the problems associated with conventional sewing processes.
For example, hot melt adhesives have been proposed as a substitute for sewing thread in various textile manufacturing processes. Hot melt adhesives include thermoplastic materials, such as polyester-, polyvinylacetate-, polyamide- and polyethylene-based resins, which quickly melt upon heating and then return to a solid material to provide an adhesive bond on cooling. When used to construct textile articles, however, conventional hot melt adhesives form bonds that cannot be optimized for aesthetic properties, such as stiffness, rigidity and flexibility; chemical resistance (particularly to chemicals to which bedding, apparel and the like may be exposed during washing, bleaching, dry cleaning, and the like); thermal resistance; discoloration; odor; open time; green strength and ultimate cure strength; manufacturing convenience; and cost.
Hot melt adhesive can be useful in the production of disposable nonwoven products, which typically are used once and then thrown away. However, woven and knit textile products constructed using conventional hot melt adhesives typically may not be durable to withstand multiple launderings, or they may possess undesirable aesthetics.
Crosslinkable or thermosetting adhesives can be applied to textile products for various purposes. These types of adhesive systems, however, also can suffer drawbacks and typically are difficult to use. For example, in the absence of clamps, supports or fixturing devices, the initial bond strength of such adhesives can be insufficient to secure textile substrates to withstand downstream processing until a complete cure is reached several hours after application. Further, thermoset adhesives often have undesirable aesthetic properties such as poor flexibility, brittleness, color and odor.
Defensive publications T926,006 and T926,010 each describe apparatus and methods for seaming a material with a hot melt adhesive which include bringing a ply of sheet material into an overlying, aligned position with another ply, applying hot melt adhesive simultaneously to each of the plies immediately as it is extruded, and then pressing the plies together prior to solidification of these deposits of adhesive. These publications, however, do not recognize nor address the practicalities associated with the properties of hot melt adhesives that are used to form seams in textile fabrics, including poor durability, flexibility, visual aesthetics, extended fixturing, and the like.
U.S. Pat. Nos. 4,251,312 and 4,186,043, each to Ziegler, Jr., et al., describe a method and apparatus for hemming a fabric using a hot melt adhesive. To hem the fabric using hot melt adhesives, the fabric is preheated prior to application of the adhesive. This is stated to overcome the problems associated with the use of hot melt adhesives in textile applications, such as insufficient bond strength to withstand handling and laundering, bleed-through of the adhesive, and the like.
Various other patents disclose the use of xe2x80x9cgluexe2x80x9d or adhesive filaments to hem or join fabrics. See, for example, U.S. Pat. Nos. 3,654,015 to Purcell, et al.; 3,963,548 to George, et al.; and 4,650,532 to Kloehn, et al. None of these patents, however, recognizes or addresses the problems associated with adhesive processes used to replace conventional sewing thread seaming and joining operations, such as durability of the adhesives, flexibility of cured adhesives, and the like.
The present invention provides threadless sewing processes for manufacturing textile products in which curable hot melt adhesives replace sewing thread in textile seaming, joining or like sewing operations. The textile products can be produced at increased speeds as compared to conventional sewing thread assembly lines. The resultant textile products are durable (i.e., can withstand multiple launderings without significant loss of strength) but nevertheless can exhibit desirable aesthetics, such as flexibility, drapeability, and softness comparable to textile products formed using conventional sewing processes. Thus, the threadless sewing processes of the invention can be used with numerous fabrics including lighter weight fabrics, such as are often used with sheeting and apparel.
In the invention, a molten, curable hot melt adhesive is applied to a surface of a textile substrate along a simulated sewing path. The curable hot melt adhesive changes its initial thermoplastic properties as a result of a chemical reaction that is initiated during or subsequent to the conditions of simulated sewing causing an irreversible increase in the initial softening point of the adhesive. Preferably, the curing takes place over a period of time, advantageously ranging from one or several hours to several days.
Curable hot melt adhesives include adhesives which react or cure to a substantially fully thermoset state and which cannot be remelted without initiating thermal degradation of the adhesive. Curable hot melt adhesives also include adhesives which upon curing exhibit an irreversible increase in softening point but which still exhibit thermal reversibility between solid and liquid phases without substantial thermal degradation.
Following application of the molten adhesive and prior to curing thereof, pressure is applied along the simulated sewing path to cause the adhesive applied along the sewing path to penetrate into the fibrous structure of the textile fabric and to affect chemical and/or mechanical interaction of the fibers of the textile fabric with the curable hot melt adhesive. In its initially solidified but uncured state, the adhesive forms a threadless seam securing fabric surfaces together at a substantial xe2x80x9cgreenxe2x80x9d strength so that the resultant article can be directed to additional downstream processing without supplemental fixturing. Because the bond preferably is not yet fully reacted, the seam can be reopened by heating and the fabric surfaces realigned or xe2x80x9cmendedxe2x80x9d if needed.
The adhesive forming the threadless seam then is subjected to conditions sufficient to react or cure the adhesive to cause an irreversible increase in the initial softening point of the adhesive and to increase the durability and/or strength of the seam. As noted above, the adhesive can cure to an essentially thermoset state or to a state which exhibits an irreversible increase in softening point, but also exhibits thermal reversibility between solid and liquid phases.
Following cure of the adhesive, the resultant seam is capable of withstanding multiple launderings without significant loss of strength. Nevertheless, the seam also can exhibit desirable aesthetic properties, such as drapeability, flexibility, and softness, in contrast to seams formed using sufficient quantities of conventional hot melt or thermoset adhesives for providing a seam of acceptable durability.
The invention is applicable to form numerous different functional and decorative threadless seams. In one aspect of the invention, the curable hot melt adhesive is applied between overlapping layers of a single, folded textile fabric to adhesively secure the layers to provide a threadless seam forming a durable hem. Alternatively, the adhesive can be applied between adjacent surfaces of two or more textile fabrics to construct a durable adhesive seam securing the textile fabrics to one another. The curable hot melt adhesive also can be applied along an edge portion of a textile fabric to provide various other types of threadless seams including a flexible, yet durable, chemical selvage, or an overedge or serge effect (especially for side hems). Still further, a shaped deposit of adhesive can be applied along an edge of a textile fabric to provide decorative threadless seams to replace various conventional decorative effects, such as perling, ribbon-hemming, piping, and other decorative finishes.
In a preferred embodiment of the invention, the adhesive is a moisture curable hot melt adhesive, and more preferably a moisture curable hot melt polyurethane adhesive. This type adhesive is initially thermoplastic but can react with moisture present in the atmosphere as humidity to irreversibly increase the initial softening point of the adhesive.
The present invention also provides textile articles constructed using curable hot melt adhesives applied to a textile article along a simulated sewing path.